Where is mechanical treatment of boiler feedwater primarily performed?

The mechanical treatment of boiler feedwater is primarily performed in the de-aerator (D.A.) tank. This is because the de-aerator plays a crucial role in removing dissolved gases, particularly oxygen and carbon dioxide, from the water before it enters the boiler system. By doing so, it minimizes the risk of corrosion within the boiler, which can otherwise lead to significant maintenance issues and efficiency losses.

In the de-aerator tank, the water is heated and subjected to a steam environment, allowing for effective separation of gases through a combination of heat and pressure. This process enhances water quality and prepares it for further treatment before it reaches the boiler. Therefore, this understanding of the function of the D.A. tank highlights why it's essential for the mechanical treatment of boiler feedwater.

Options that suggest external treatment or specific temperature ranges, while potentially relevant in other contexts, do not specifically reference the principal environment where this critical mechanical treatment occurs. The D.A. tank is specifically designed for this purpose, making it the most accurate answer.